1. Field of the Invention
The present invention relates to the drilling of tunnels through earth or rock formations. In particular it pertains to tunneling shields for shielding portions of the tunnel at or near tunnel boring machines which are being used to drill such a tunnel.
2. Description of the Prior Art
Various types of tunnel boring machines are employed to drill tunnels through subterranean formations. One especially efficient type of tunnel boring machine comprises a cutterhead assembly, including a plurality of cutters mounted on its forward face for contacting the earth formation. The cutterhead assembly is rotatably mounted on a cutterhead support assembly. The cutterhead support assembly is in turn fixed to a main frame which extends axially away from the cutterhead support in a rearward direction. A gripper assembly is mounted on the main frame so that it can slide longitudinally therealong.
The gripper assembly may include a pair of grippers mounted on a carriage which is non-rotatable relative to the main frame. The grippers are radially extensible to engage the tunnel wall. The gripper and cutterhead support assemblies are connected by advancement means, such as piston and cylinder assemblies. When the grippers are engaged with the tunnel wall, the main frame, cutterhead support and cutterhead assemblies may be driven forward relative to the grippers by the advancing means to urge the cutters against the tunnel face. Simultaneously, the cutterhead assembly is rotated by suitable power means, moving the cutters across the face of the tunnel. The grippers remain fixed against the tunnel wall to provide reaction for the drilling forces. Buckets mounted along the periphery of the cutterhead, scrape along the invert of the tunnel picking up fragments of rock and dirt which have been broken from the tunnel face by the cutters. When the buckets reach the top of their circular path, they drop these cuttings onto a conveyor which transports them to the rear of the machine once they are removed from the tunnel.
Drilling proceeds in this manner until the main frame reaches the end of its travel with respect to the gripper assembly. At this time the grippers are retracted from the tunnel wall and the drive means is reversed to pull the gripper assembly forward along the main frame. Then the grippers are once again extended into engagement with the tunnel wall, and the cycle is repeated. This type of tunnel boring machine is described in detail in U.S. Pat. No. 3,596,445-Winberg and the above mentioned copending patent application Ser. No. 363,057, now U.S. Pat. No. 3,859,810.
One of the problems encountered in boring tunnels with such machines, or any other type of machine, is the problem of falling rock, dirt, etc. from the top or crown of the tunnel as drilling progresses. Many times the tunnel is lined behind the drilling machine or provided with some sort of roof support to prevent the tunnel from caving in and hinering operations, damaging the machine or injuring workers in the tunnel. However, it is difficult, if not almost impossible, to provide such linings or roof supports directly above the tunneling machine while drilling progresses. Thus, there is a possibility of rocks and dirt falling from the crown of the tunnel into the machine or on the workers operating such a machine.
In the type of machine previously discussed herein, this problem is particularly acute in the area of the tunnel between the gripper assembly and the cutterhead support assembly. Since the space between the gripper and cutterhead support assemblies varies considerably during the drilling cycle, it is extremely difficult to provide protection from falling rocks.
Various types of tunneling shields have been devised for protecting areas of tunnel boring machines during their operation. For example, U.S. Pat. No. 3,301,600 Pirrie et al. discloses a cylindrical shell-like shield which is mounted on the cutterhead support assembly. Such a shield provides good protection for the cutterhead support assembly but provides no protection behind the cutterhead support assembly. Tunnel liners must be installed to provide this protection.
Another shell type shield is disclosed in U.S. Pat. No. 3,377,105--Wallers. Although it does appear that some protection is provided between a cutterhead support assembly and rearward parts of the tunnel boring machine, the shield of Waller provides little flexibility and would not appear to permit angular movement of the cutterhead support assembly relative to other portions of the machine. Another tunneling shield is shown in U.S. Pat. No. 3,467,463--Pentith et al. However, the shield disclosed in this patent provides protection only over the main frame area. No shielding is provided between the main body of the machine and the cutter.